Karl Anders Petrén (1868-1927) was a Swedish physician who was a native of Halmstad. He studied medicine under Magnus Blix (1849-1904) in Sweden and Joseph Jules Dejerine (1849-1917) in Paris. He received his doctorate in 1896, and was later a professor of practical medicine in Uppsala and Lund.
Petrén is remembered for his work with diabetes prior to the days of readily available insulin. He noticed that adding meat to the diet of diabetic individuals sometimes exacerbated or induced ketosis, whereas a diet with a high fat content reduced ketosis. He demonstrated that if protein intake was limited, and the amount of fat in the diet was large enough, ketosis in diabetes could be eliminated.
In 1901, Petrén published an important treatise on gait disorders titled Uber den Zusammenhang zwischen anatomisch bedingter und functioneller gangstorung im Greisenalter, in which he describes a condition called trepidant abasia or "trembling abasia".